Effect of alloyed Lu, Hf and Cr on the oxidation and spallation behavior of NiAl

The influences of alloyed Lu, Hf and Cr on the oxidation and spallation behavior of NiAl were investigated. Although Lu has a “block effect” of Al as Hf does, the oxidation rate of Lu-doped NiAl is significantly higher, due to: (1) inhibitation of θ- to α-Al2O3 transformation in early oxidation stage; (2) stronger scale grain refinement effect and enhanced oxygen transport rate. Segregation of S and C occurs not only at the alloy/scale interface, but also within the scale. Both Lu and Hf can significantly improve the scale adherence. However, This beneficial effect can be easily overcompensated by Cr.